1. Field of the Invention
The present invention relates to a flame retardant comprising a brominated styrene or styrene derivative polymer having acid anhydride groups. Further, the present invention relates to a flame-resistant polyamide resin composition comprising the flame retardant. Said composition is mainly used in electrical and electronic fields.
2. Discussion of Related Art
Polyamides, because of their high thermal resistance and mechanical characteristics, are successfully used in the electrical and electronic fields. In these fields, a high degree of flame resistance is required for resin materials by the UL Regulation of the United States. To make polyamides flame-resistant, there have been used nitrogen-containing flame retardants (e.g. melamine cyanurate), halogen-containing flame retardants (e.g. octachlorine adduct of cyclopentadiene, brominated polyphenylene ether, brominated polystyrene), etc. Among these, melamine cyanurate is such a poor flame retardant that it is difficult to make glass fiber-containing compositions highly flame-resistant. Among the halogen-containing flame retardants, the former two are inferior in thermal stability to the brominated polystyrene. At the present time, brominated polystyrene is the best known flame retardant for rendering polyamides flame-resistant.
As to brominated polystyrene and flame-resistant compositions comprising polyamides and brominated polystyrene, there are known JP-A-51-47034, JP-A-51-47044, JP-A-57-53505, JP-A-61-34058, and U.S. Pat. Nos. 4,137,212 and 4,373,049.
Also, as examples of compositions which are not flame-resistant, but are superior in mechanical strength, these compositions which comprises a polyamide and a copolymer of styrene or a styrene derivative and an unsaturated carboxylic acid anhydride, are disclosed in JP-A-56-50931, JP-A-60-86162 and JP-A-60-19517.
It was found, however, that the polyamide compositions with brominated polystyrene as a flame retardant have a serious drawback in that thin molded products which are made of these compositions are inferior in strength at the weld portion. A connector, one of the important parts in the electrical and electronic fields, has a hole for pin insertion at the very weld portion. When the weld strength of the material is low, there occurs a problem that cracks are produced when a pin is forced into the hole.